1. Field of the Invention
This invention relates generally to a solid state television camera, and is directed more particularly to a solid state color television camera in which color difference signals obtained from a spacial color filter in a line sequential manner are converted simultaneously to a standard color signal.
2. Description of the Prior Art
In the art there have been proposed various solid state color television cameras which use a semiconductor element such as a bucket brigade device (BBD), charge coupled device (CCD) or the like as its solid state image sensing device. Also, various color filters which are disposed at the front of the solid state image sensing device have been well known. One of the well known color filters, for example, a so-called double-green type filter, which includes a greater amount of the green color component to be more appealing to the eye than those of the other color components forming the luminance signal, is used to improve the resolution.
This double-green type color filter has a plurality of transparent or light transmissibility regions whose unit area corresponds to one picture element. In this case, the region corresponding to an odd horizontal scanning line is so selected that it contains the green color component G twice as compared with the red and blue color components R and B. For example, the transparent regions of G, R and B are arranged in a horizontal scanning line in the order of G-R-G-B which is repeated sequentially.
For an even horizontal scanning line, due to the signal process described later, the position of the transparent regions are so selected that the green color component G is reversed in phase with respect to the odd horizontal scanning line.
Accordingly, when an object is picked up by a camera using the above filter, the spectra and phase relation of the respective color components become as follows.
If the sampling frequency in the horizontal scanning direction is selected as f.sub.C, and the band of the green color component G is selected at a sampling frequency f.sub.C of 4.5 MH.sub.z, the sampling output relating to the green signal includes, in addition to a modulating signal component (DC components or base band components) S.sub.DG, a side band component (AC component) S.sub.MG whose carrier is the sampling frequency f.sub.C. If sampling frequency f.sub.C is about 4.5 MH.sub.z as set forth above, the relationship of the signal bands becomes such that side band component S.sub.MG is mixed into modulating signal component S.sub.DG to cause a sampling error. This sampling error caused by side band component S.sub.MG deteriorates the reproduced picture. The sampling error is removed by utilizing the vertical correlation process. That is, since the phases of carriers obtained from adjacent horizontal scanning lines are opposite, the sampling error can be removed by vertical correlation.
The carriers of the respective red color component R and blue color component B are just one-half that of the green color component G, so that in the case of the green component G, side band components cannot be removed by the vertical correlation process since the phases of the carriers are not opposite.
It is difficult to limit the pass band of only a desired color signal by an optical device, that is, to form an optical low pass filter for the purpose of removing the undesirable effects of the side band components.